Transcript BasicRefrigerationandChargingProcedures

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BASIC REFRIGERATION
&
CHARGING PROCEDURES
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SECTION ONE
REFRIGERANT
PRESSURES, STATES
&
CONDITIONS
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Load out to ambient
Load in
from house
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Heat flows from hot to cold.
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Evaporator Side Terms
Evaporating Pressure
Low Side Pressure
Suction Pressure
Back Pressure
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Condenser Side Terms
Condensing Pressure
Head pressure
High side pressure
Discharge pressure
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Compressor
 Pumps refrigerant vapor only!
 Divides low and high side.
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Discharge Line
 Connects the compressor
to the condenser.
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Condenser
 Rejects heat from the refrigerant.
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Liquid Line
 Supplies liquid refrigerant
from the condenser to the
metering device.
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Metering Device
 Controls the flow of refrigerant.
 Divides low and high side.
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Evaporator
 Absorbs heat into the refrigerant.
Removes moisture from the air
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Suction Line
 Returns superheated vapor from
the evaporator to the compressor
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Receiver
An accessory added in the liquid
line to store refrigerant for different
loads placed on the system.
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CONDENSER
Temperatures
Pressures
States
CONDENSER INLET

High Pressure
High Temperature 
Superheated Vapor
Saturation Point

(vapor changing to a
liquid as heat is removed)
Near Ambient Temperature
High Pressure

Subcooled Liquid
OUTLET

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EVAPORATOR
Temperatures
Pressures
States
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Evaporator
inlet

Low Pressure
Low Temperature
About 80% Liquid,
20% Vapor
Saturated vapor 
(Temperature in
which liquid is
changing to a
vapor)

Evaporator
Outlet
Low Pressure
Low Temperature
Superheated Vapor
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SECTION TWO
SUBCOOLING
&
SUPERHEAT
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Subcooling and Superheating
The concepts of subcooling and
superheating are the two most
important principles that the
service technician must understand
before attempting to systematically
troubleshoot hvac/r systems.
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210 psig = 105 ºF
-100 ºF
Subcooling 5 ºF
R-22
Condenser Subcooling
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TOTAL
SUBCOOLING
210 psig = 105 ºF
-95 ºF
Subcooling 10 ºF
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Superheat
Superheat is any heat added to completely
saturated vapor that results in a rise in
temperature (sensible heat change) of the gas.
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60 °F
76 psig = 45 °F
15 °F
superheat
Evaporator Superheat
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Total or System
Superheat
Suction line
Temperature 60°F
76 psig =
45°F
Superheat
15°F
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SECTION THREE
METERING
DEVICES
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Capillary Tube
Automatic Expansion
Valve
Thermostatic Expansion
Valve
Fixed –Bore Piston
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Capillary Tubes
 Low Cost device
 Have no moving parts
 Can be used on a wide range
of applications
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Thermostatic Expansion Valve
 Most efficient
 Maintains a constant evaporator
superheat
 Helps prevent compressor
flooding
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TXV Types

Pressure Limiting

Balance Port


Externally equalized

Internally Equalized
Electric operated
TXV Bulb Placement
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TXV External Equalizer Tap Location
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Automatic Expansion Valves

Maintain a constant evaporator
pressure

Used on small systems which
have constant loads
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Fixed-Bore Metering Devices

Most common today on Residential
systems

Dual purpose device
Works as metering a device
Works as a check valve

Critical charge
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SECTION FOUR
System CHARGE
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Is The Refrigerant Charge Correct?
 All refrigeration systems differ in the
amount of charge they hold.
 There are guidelines, charts, and
techniques to follow.
 System design & layout must be known
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How long & what size
is the line set?
What’s the volume of
the filter drier?
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TXV CHARGING RULES
1. Charge system under a high load
2. Charge as a liquid when possible
3. Throttle liquid blends into low side
4. Record evaporator & compressor
superheat & Condenser subcooling
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AIRCONDITIONING SYSTEMS
Capillary Tube
or
Fixed Orifice
#1 Weigh in the correct charge
#2 Manufacture's charging charts
#3 Use system superheat method
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Requirements for system
superheat charging

Proper evaporator air flow

Accurate remote bulb temperature tester

Accurate gauge manifold set
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What should the Superheat be?

SYSTEM SUPERHEAT CHARGING
Indoor Wet-Bulb Air Temperature
65ºF
Condenser
70ºF
Entering
75ºF
Air
80ºF
Temperature
85ºF
90ºF
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60
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72 74
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
95ºF
100ºF
To increase superheat remove
refrigerant.

To decrease superheat add
refrigerant.
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System Superheat
Suction line
Temperature 60 °F
76 psig = 45
°F
Superheat 15 °F
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AIR FLOW
Can be measured in many ways
1. Equipment data charts
2. Air flow meters
3. Combination of
meter readings and
formulas
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Sensible Heat Formula
CFM =
Sensible heat BTU’s
1.08 X temperature
difference
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Sensible Heat Formula
Electric Heat
BTU’s = Heater amps X volts X 3.41
Sensible
heat
BTU’s
CFM =
1.08 X temperature
difference
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Sensible Heat Formula
3 Phase Electric Heat
BTU’s = Heater amps X volts X 3.41 X 1.73
Sensible
heat
BTU’s
CFM =
1.08 X temperature
difference
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Sensible Heat Formula
Fossil Fuel Heat
BTU’s = Heater input X Efficiency
or
Bonnet capacity
CFM =
Sensible heat BTU’s
1.08 X temperature
difference
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Measuring Duct Velocity
CFM = Velocity X Area in square feet
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SAMPLE
QUESTIONS
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The high and low pressures in a
refrigeration system are separated by:
a.
The compressor.
b.
The evaporator.
c.
The metering
metering device.
device.
The
d.
The filter drier.
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Subcooling can be defined as:
a.
The cooling effect of an evaporator.
b.
Any sensible heat removed from 100%
saturated liquid.
c.
The superheat that is removed at the top of
the condenser.
d.
The cooling of the compressor motor by
returning refrigerants.
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Always charge a TXV with a receiver and
sightglass under a:
a.
No load condition.
b.
Low load condition.
c.
High load condition.
d.
None of the above.
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Superheat is defined as:
a. The heat added the the saturated
liquid.
b. Heat removed from the saturated
liquid in the condenser.
c. The heat added to the saturated
vapor
vapor exiting
exiting the
the evaporator.
evaporator.
d. The heat removed from the saturated
vapor exiting the evaporator.